how much does it cost to get into Michigan Adventures?

Question

and do they make adults pay even if there not going on the rides?

Answer 1

$24. And yes, they make you pay even if you are not going on the rides. There is no way for the park to keep track of those who entered that are going on the rides and those that are not.

Given that, you don't need to go on any rides to enjoy the park. Just hang out at the water park, take a dip in the wave pools, lounge in the lawn chairs, etc.